The present invention relates to photosensitive polyimide precursor compositions useful for forming relief structures on silicon, glass, ceramic, or polymer substrates bearing copper or silver circuitry. The photosensitive compositions according to this invention are especially suitable for applications in microelectronics.
Negative tone photosensitive polyimide precursors based on polyamic esters containing radiation sensitive groups in the ester moiety are well known (U.S. Pat. Nos. 4,040,831, 4,548,891, 6,010,825). When these polymers are formulated with a radical photoinitiator and a cross-linking agent in a suitable solvent, the resulting material may be processed as a negative tone photoresist. The photoimaging and processability of these resist compositions may be modified by adding to the formulation one or more compounds such as adhesion promoters, photosensitizers, dyes, leveling agents, and viscosity stabilizing agents. Many formulations of this type are known and are widely used in the microelectronic industry. Microelectronic applications include, but are not limited to, stress relief layers for packaged microelectronic devices, protective coatings, alpha particle barrier coatings, and as dielectric layers. Substrate materials that have been processed with photosensitive polyimide coatings include silicon device wafers, ceramics, glass, flexible polymer-metal foils, and the like.
In use, the polyamic ester formulations are coated as a film on a substrate using any of a variety of coating methods including spin, dip, spray, roller, meniscus, extrusion, and curtain coating. The resulting wet film is heated at temperatures ranging from 50 to 150xc2x0 C. to provide a tack-free or xe2x80x9csoftbakedxe2x80x9d film. The softbaked film is then exposed to the action of actinic rays at wavelengths ranging from 350 to 450 nanometers through a photomask. Such actinic rays are commonly obtained from the mercury lamp whose most useful rays are the i-line at 365 nanometers and the g-line at 436 nanometers. The actinic rays interact with the photoinitiator in a photochemical reaction to produce an organic radical that initiates a radical cross-linking reaction of the unsaturated groups of the polyamic ester and the crosslinking agent. The products of this reaction have decreased solubility in certain solvents. Thus, treatment of the exposed film with an appropriate solvent results in the removal of unexposed areas and the retention of exposed areas to form a relief pattern of the mask in the film. After image development, the patterned polyamic ester film is converted to a patterned polyimide film by the means of applying heat at temperatures ranging from 200xc2x0 C. to 450xc2x0 C. for a period of time ranging from thirty minutes to six hours.
The efficacy of the photochemical cross linking reaction in producing an insoluble product is known to be adversely affected by the presence of chemicals that react with the radicals produced by the photoinitiator in such a manner as to prevent or inhibit the cross linking of the polymer. When crosslinking inhibition occurs, the relief image is damaged or lost during the image development process and film loss during development is high. A well-known example of such an inhibitor is the oxygen molecule, which inhibits the photocrosslinking of polyamic acrylate esters and is well known as an inhibitor toward the radical polymerization of acrylate and acrylate derivatives. Inhibition of crosslinking also occurs when photosensitive polyimide precursor formulations containing certain organotitanocene photoinitiators are processed on substrates wherein copper and silver metal layers are present. Lowering the softbake temperature of the spin applied coating can lessen the undesirable inhibition effects on copper and silver layers. However, this approach decreases pattern resolution and results in unacceptably fast photospeeds and increased film loss. The increased industrial use of copper and silver metal as the conductor in microelectronic devices, sensors, packages, and flexible circuit elements has created a need for formulations with improved performance where copper and silver layers are present.
It is the object of the present invention to provide a negative working photosensitive polyimide precursor formulation whose photoimaging function is not inhibited when the composition is applied to and processed on copper or silver bearing substrates. The photosensitive composition of this invention consists of a polyamic ester polymer containing ethylenically unsaturated groups, a photocrosslinking additive, a photoinitiator, a metal inhibitor, a polymerization inhibitor, and a solvent. Optionally and in addition to the aforementioned components, the composition may contain one or more photosensitizers, adhesion promoters, and dyes.
The photosensitive compositions can be used in the manufacture of microelectronic devices and in electronic applications such as thermal and mechanical stress buffer coatings, alpha particles barrier coatings, interlayer dielectric films, and as patterned engineering plastic layers.
One aspect of the present invention is to provide a photosensitive polyimide precursor composition comprising:
(i) 20-50 parts by weight of a polyamic ester polymer (C) obtained by the polycondensation of a diester-diacid chloride compounds (A) with a diamine compound (B).
(ii) 1-4 parts by weight of a photoinitiator (D).
(iii) 3-10 parts by weight of a photocrosslinkable additive (E).
(iv) 0.005-1 parts by weight of a metal inhibitor (F).
(v) 0.01-1 parts by weight of a polymerization inhibitor (G).
(vi) 44-76 parts by weight of a solvent (H).
Optionally and in addition to components A and D through H inclusively, the composition may contain one or more of the following components:
(vii) 0.1-2.0 parts by weight of one or more photosensitizer compounds (I).
(viii) 0.05-2.0 parts by weight of an adhesion promoting compound (J).
The polyamic ester polymer (C) has a number average degree of polymerization of 5 to 100 and is synthesized by the polycondensation of monomers A and B as follows (1): 
Monomer A is obtained by the reaction of a dianhydride compound with at an alcohol, Rxe2x80x2OH, to yield a diester-diacid followed by conversion of the diacid-diester to a diester-diacid chloride by means of a suitable reagent (Formula 2). 
The group R represents a tetravalent aromatic group containing at least one 6-membered carbon ring wherein the four carbonyl groups are directly connected to is different carbon atoms of R and wherein each of two pairs of the four carbonyl groups is connected to adjacent carbon atoms. The dianhydride compound may be selected from one or more of the following dianhydrides: pyromellitic dianhydride (PMDA), 3,3xe2x80x2, 4,4xe2x80x2-benzophenonetetracarboxylic dianhydride (BTDA), 3,3xe2x80x2, 4,4xe2x80x2-biphenyltetracarboxylic dianhydride (BPDA), 3,3xe2x80x2, 4,4xe2x80x2-diphenylsulfonetetracarboxylic dianhydride, 4,4xe2x80x2-perfluoroisopropylidinediphthalic dianhydride (6FDA), 4,4xe2x80x2-oxydiphthalic anhydride (ODPA), bis (3,4-dicarboxyl) tetramethyldisiloxane dianhydride, bis(3,4-dicarboxylphenyl)dimethylsilane dianhydride, cyclobutane tetracarboxylic dianhydride, and 1,4,5,8-naphthalenetetracarboxylic dianhydride. The tetracarboxylic dianhydrides can be used singly or in combination and selection of the dianhydride compound is not limited to the compounds listed above. The group Rxe2x80x2 contains at least one unsaturated group which may be a vinyl, allyl, acrylyl, methacryl, acetylenic, a cyano group, or other suitable radiation crosslinkable group.
Monomer B is an divalent diamine wherein the group R1 contains at least one 6-membered carbon ring and is selected from at least one the following group of divalent aromatic, heterocyclic, alicyclic or aliphatic amines: m-phenylenediamine, p-phenylenediamine, 2,2xe2x80x2-bis(trifluoromethyl)-4,4xe2x80x2-diamino-1,1xe2x80x2-biphenyl, 3,4xe2x80x2-diaminodiphenyl ether, 4,4xe2x80x2-diaminodiphenyl ether, 3,3xe2x80x2-diaminodiphenyl ether, 2,4-tolylenediamine, 3,3xe2x80x2-diaminodiphenyl sulfone, 3,4xe2x80x2-diaminodiphenyl sulfone, 4,4xe2x80x2-diaminodiphenyl sulfone, 3,3xe2x80x2-diaminodiphenylmethane, 4,4xe2x80x2-diaminodiphenylmethane, 3,3xe2x80x2-diaminodiphenylmethane, 3,4xe2x80x2-diaminodiphenylmethane, 4,4xe2x80x2-diaminodiphenyl ketone, 3,3xe2x80x2-diaminodiphenyl ketone, 3,4xe2x80x2-diaminodiphenyl ketone, 1,3-bis (4-aminophenoxy) benzene, 1,3-bis(3-amino-phenoxy) benzene, 1,4-bis (xcex3-aminopropyl)tetramethyldisiloxane, 2,3,5,6-tetramethyl-p-phenylenediamine, m-xylylenediamine, p-xylylenediamine, methylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, 2,5-dimethylhexamethylenediamine, 3-methoxyhexamethylenediamine, heptamethylenediamine, 2,5-DIMETHYLHEPTAMETHYLENEDIAMINE, 3-methylheptamethylenediamine, 4,4-dimethylheptamethylenediamine, octamethylenediamine, nonamethylenediamine, 2,5-dimethyinonamethylenediamine, decamethylenediamine, ethylenediamine, propylenediamine, 2,2-dimethylpropylenediamine, 1,10-diamino-1,10-dimethyldecane, 2,11-diaminidodecane, 1,12-diaminooctadecane, 2,17-diaminoeicosane, 3,3xe2x80x2-dimethyl-4,4xe2x80x2-diaminodiphenylmethane, bis(4-AMINOCYCLOHEXYL)METHANE, 3,3xe2x80x2-diaminodiphenylethne, 4,4xe2x80x2-diaminodiphenylethylene, and 4,4xe2x80x2-diaminodiphenyl sulfide, 2,6-diaminopyridine, 2,5-diaminopyridine, 2,6-diamino-4-trifluoromethylpyridine, 2,5-diamino-1,3,4,-oxadiazole, 1,4-diaminocyclohexane, piperazine, 4,4xe2x80x2-methylenedianiline, 4,4xe2x80x2-methylene-bis(o-choloroaniline), 4,4xe2x80x2-methylene-bis(3-methylaniline), 4,4xe2x80x2-methylene-bis(2-ethylaniline), 4,4xe2x80x2-methylene-bis(2-methoxyaniline), 4,4xe2x80x2-oxy-dianiline, 4,4xe2x80x2-oxy-bis-(2-methoxyaniline), 4,4xe2x80x2-oxy-bis-(2-chloroaniline), 4,4xe2x80x2-thio-dianiline, 4,4xe2x80x2-thio-bis-(2-methylaniline), 4,4xe2x80x2-thio-bis-(2-methyoxyaniline), 4,4xe2x80x2-thio-bis-(2-chloroaniline), 3,3xe2x80x2sulfonyl-dianiline, 3,3xe2x80x2sulfonyl-dianiline. The selection of monomer B is not restricted to these compounds and the monomers B can be used singly or in combination.
Photoinitiator D is selected from at least one of the group consisting of. 
namely, bis(.eta. 5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl) titanium and bis(methylcyclopentadienyl)-bis(2,6-difluorophen-1-yl)titanium.
Photocrosslinking agent (E) is selected from at least one of the group consisting of esters and partial esters of acrylic acid or methacrylic acid and aromatic and particularly aliphatic polyols with 2-30 C-atoms or cycloaliphatic polyols with 5 or 6 C-atoms. Examples of suitable components (E) are: ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol di(meth)acrylates with an average molecular weight in the range of 200-2000, trimethylolpropane ethoxylate tri(meth)acrylates with an average molecular weight in the range of 500-15000, pentaerythrite tri(meth)acrylate, pentaerythrite di(meth)acrylate, pentaerythrite tetra (meth)acrylate, and the like.
The metal inhibitor compound (F) is selected from at least one of the group consisting of: 1H-tetrazole, 1,2-cyclohexanediamine tetraacetic acid hydrate, and 5mercaptobenzimidazole.
The polymerization inhibitor (G) is selected from the group consisting of para-benzoquinone, thiodiphenylamine, and alkyl phenols such as 4-tert-butylphenol, 2,5-DI-TERT-BUTYL hydroquinone, or 2,6-di-tert-butyl-4-methylphenol.
The solvent (H) is selected from the group consisting of 2-methylpyrrolidone, xcex3-butyrolactone, N, N-dimethylformamide, N,N-dimethylacetamide, dimethylsufoxide, sulfolane, ethylene glycol monomethyl ether, cyclopentanone, propylene glycol monomethyl ether acetate, and tetrahydrofuran. These solvents may be used separately or as mixtures.
The compositions embraced by this invention may optionally contain one or more of the following components in addition to polymer A and components D through H.
One or more photosensitizers (I) selected from the group consisting of coumarins of Formula 5 
in which R3 and R4, independent of one another, are C1-C6 alkyl groups and R5 indicates C1-C6 alkylcarbonyl, C1-C6 alkoxycarbonyl, C6-C14 arylcarbonyl, or C6-C14 aryloxycarbonyl, optionally substituted with C1-6 dialkylamino substituents.
One or more adhesion promoting compounds (J) selected from the group consisting of aminoalkoxysilanes and derivatives of aminoalkoxysilanes.
The formulated compositions may also contains additives such as pigments, colorants, fillers, adhesives, wetting agents, and dyes that can influence the spectral sensitivity of the mixtures by their intrinsic absorption.
As the first step in applying the photosensitive polyimide precursors compositions embraced by this invention, the photosensitive composition is coated on a substrate such as a silicon device wafer, a ceramic substrate, a flexible polymer substrate, and the like which may have copper or silver metal films coated or attached to them by means of an adhesive. Coating methods suitable for use include but are not limited to spin coating, roller coating, offset printing, screen printing, extrusion coating, meniscus coating, curtain coating, dip coating, and spray coating. The resulting wet coating is dried or softbaked at a temperature of 70 to 150xc2x0 C. using a hot plate, convection oven, belt furnace, and the like for a period of several minutes to twelve hours depending on the coating method and film thickness. The dried coating is exposed to actinic rays through a mask pattern in a manner such that an image of the mask pattern is formed in the dried film. Examples of actinic rays useful in the practice of this invention are x-rays, electron beams, ultraviolet rays, and visible light rays. The most preferred rays are those with wavelengths of 365 nanometers and 436 nanometers and are readily obtained from mercury lamp sources.
In the next step, the imaged film is developed to form a relief image of the mask pattern by treating the exposed film with an appropriate solvent. Examples of solvents useful in the practice of this invention include but are not limited to xcex3-butyrolactone, 2-methylpyrollidone, n-butyl acetate, ethyl lactate, cyclopentanone, cyclohexanone, propylene glycol monomethyl ether acetate, isopropanol and binary or ternary mixtures thereof. Image development can be carried out by means of immersion, spray, puddle, spray-puddle, or similar means known in the photoresist art. The developed relief pattern is rinsed with a solvent suitable for removal of the developer solvent. Rinse solvents useful in the practice of this invention include but are not limited to n-butyl acetate, propylene glycol monoethyl ether acetate, and isopropanol. The relief image is then converted to a patterned polyimide film by applying heat at temperatures ranging from 200 to 425xc2x0 C. for times ranging from 30 minutes to six hours.